1. Field of the Invention
The present invention relates to a method and an apparatus of fabricating a liquid crystal display device.
2. Description of the Related Art
A liquid crystal display device comprises first and second substrates, and a liquid crystal inserted between the substrates. One of the first and second substrates is a TFT substrate supporting TFTs, for example, and the other substrate is a color filter substrate supporting color filters. The first substrate is formed with a peripheral seal made of a photo-curable sealing material, and the peripheral seal is set by being irradiated with ultraviolet light after the first and second substrates are joined together. The liquid crystal is arranged in an area surrounded by the peripheral seal.
In the conventional method of fabricating a liquid crystal display device, an injection hole is formed in the peripheral seal and, after joining the first and second substrates together, a liquid crystal is injected in a vacuum chamber through the injection hole formed in the peripheral seal. After that, the injection hole of the peripheral seal is closed, and the liquid crystal panel comprising the first and second substrates is taken out of the vacuum chamber, and the peripheral seal is pressed to form an appropriate cell gap. The peripheral seal is set by being irradiated with ultraviolet light.
Japanese Unexamined Patent Publications No. 8-190099 and No. 2000-66163 disclose a method, of fabricating a liquid crystal display device, which is called a drip-injection method. In the drip-injection method, a peripheral seal is formed on the first substrate and a liquid crystal is dripped onto the substrate. Then, the first substrate and the second substrate are joined together under pressure in a vacuum chamber. After that, the pressure is released from the first and second substrates, and the first and second substrates are exposed to the atmospheric pressure. The peripheral seal is set by the ultraviolet light irradiated thereonto. According to the drip-injection method, the fabrication process is shortened and the fabrication cost of the liquid crystal display device is reduced.
In the drip-injection method, the first substrate and the second substrate are joined under pressure in a vacuum chamber. For this purpose, the first substrate and the second substrate are supported by respective support members in the vacuum chamber. These support members are called an upper surface plate and a lower surface plate. The first substrate onto which the liquid crystal is dripped is fixed to the lower surface plate, while the second substrate is fixed to the upper surface plate. The upper surface plate is movable, and the first substrate and the second substrate can be joined together under pressure in the vacuum chamber, by moving the upper surface plate toward the lower surface plate.
The first substrate and the second substrate are fixed to the upper and lower surface plates, respectively, by electrostatic chucks. The electrostatic chuck is generally used as a means for holding the substrate in the semiconductor fabrication process. The electrostatic chuck, however, sometimes has an insufficient attractive force to attract the glass substrate used as a substrate of the liquid crystal display device. Unless the surface of the glass substrate is in close contact with the surface of the electrostatic chuck, for example, the electrostatic chuck may not be able to hold the glass substrate sufficiently. In view of this, an attempt has been made to hold the glass substrate sufficiently on the upper and lower surface plates using both attraction by the electrostatic chuck and attraction by a vacuum.
In the case where means for holding the glass substrate by the electrostatic attraction and the vacuum attraction are both used, the first substrate and the second substrate are pressed and attached to each other in a vacuum environment, and the upper surface plate is moved away from the lower surface plate in such a manner as to release the pressure in the vacuum chamber, after which the vacuum chamber is exposed to the atmosphere. In the case where the pressure exerted on the substrates is released in a vacuum environment, however, the peripheral seal would be extended from the compressed state as the compressive force is removed, with the result that the peripheral seal would assume an irregular shape, thereby leading to the problems of leakage of the liquid crystal or gap failure.